Recently, terminals that can be connected to two or more different networks have been introduced. For example, terminals that can be connected to a first network such as the IEEE 802.11 or IEEE 802.16 and a second network such as CDMA, GSM, GPRS, TDMA, WCDMA or UTRAN/GERAN have been presented.
However, in spite of the launch of such terminals, technology regarding handover performed between two or more different networks, and seamless handover or handover independent from media is yet to be complete.
In particular, if the terminal, which is currently performing a session including voice and non-voice data via a first network, i.e., a WLAN, moves to an area where a second network, i.e., the UTRAN/GERAN, is available, in order to allow the terminal to continuously perform the session, the voice data in the ongoing session should be moved to a CS (Circuit Switching) domain of the UTRAN/GERAN and non-voice data in the ongoing session should be moved to a PS (Packet Switching) domain of the UTRAN/GERAN. However, an application server (AS), which handles a mobility of the session, cannot know whether the terminal wants to move both the voice and non-voice data of the session to the UTRAN/GERAN or whether it wants to move only the voice to the UTRAN/GERAN, so successful mobility of the session cannot be guaranteed. This will be described in detail with reference to FIG. 1.
FIG. 1 is a flow chart showing a method for supporting a session mobility according to the related art.
1) A UE#a 11 is performing a session including voice data and non-voice data with a UE#b 12 via the first network (original network), e.g., the WLAN (S11).
2) The UE#a 11 moves to an area where the second network (target network), e.g., the UTRAN/GERAN is available to be used (S12). In this case, the second network, e.g., the UTRAN/GERAN, includes a CS domain and a PS domain, the UE#a 11 can be connected to the both domains. Thus, it is determined that, when the UE#a 11 moves to the second network, e.g., the UTRAN/GERAN, the voice with the UE#b 12 is performed through the CS domain while the non-voice data is performed through the PS domain.
3) In order to move the non-voice data in the session in the WLAN, the UE#a 11 transmits an INVITE message to the AS (S13). Here, the INVITE message includes a Replace header. The Replace header is used to move the session in the established WLAN to the UTRAN/GERAN.
4) Upon receiving the message, the AS transmits re-INVITE to the UE#b 12 so that the UE#b 12 can update the session with respect to the non-voice data (S14).
5) Meanwhile, the UE#a 11 transmits a CS SETUP message to an MGCF through the CS domain of the UTRAN/GERAN in order to move the voice in the session in the WLAN (S15).
6) The MGCF transmits an INVITE message to the AS in response to the reception of the CS SETUP message (S16). In this case, the MGCF does not have capability of including a Replace header to the INVITE message.
7) Upon receiving the INVITE message, the AS transmits a re-INVITE message to the UE#b 12 so that the UE#a and the UE#b12 can update session with respect to the voice (S17).
Therefore, although the UE#a 11 includes the Replace header in the INVITE message and transmits the same, the Replace header indicates only the fact that the session in the established WLAN is moved to the UTRAN/GERAN without including information as to whether both the voice and non-voice data of the session should be moved or as to whether only the voice data of the session should be moved, so the AS cannot guarantee successful mobility of the session.
In detail, although the AS has received the INVITE message including the Replace header but an INVITE message by the MGCF is not received, the AS cannot recognize whether the INVITE message by the MGCF is delayed due to a bad condition of the network or whether the UE#a 11 has not transmitted it. In this case, there is high possibility that the AS misrecognizes that the UE#a 11 intends to move only the non-voice data, so the successful mobility of the session cannot be guaranteed.
In addition, although the UE#a 11 has transmitted the INVITE message including the Replace header, if the INVITE message including the Replace header arrives later than the INVITE message transmitted by the MGCF, the AS cannot recognize whether the INVITE message by the MGCF is for generating a new session or whether it is to move the established session, so a successful mobility of the session cannot be guaranteed.
Meanwhile, whenever the AS receives one of the two INVITE messages, it transmits the re-INVITE message to the UE#b 12. In this case, if the voice and non-voice data are to be moved to the UTRAN/GERAN, it would be better to transmit the re-INVITE message at a time to save network resources.